Rotary sliding vane compressor and blade therefor

ABSTRACT

Disclosed is a blade for a rotary blade compressor. The blade has at least two section pieces, with any two adjacent section pieces being radially aligned with each other at a junction, wherein further there is a force applying means at said junction forcing the adjacent blade section pieces apart from each other in an axial direction. The edges of said blade will thereby be positioned to form a seal against the head plates of the compressor.

BACKGROUND OF THE INVENTION

A “sliding” rotary vane compressor is a positive displacement machine that uses a rotor, which may be, but is not necessarily, eccentric, placed within a cylindrical chamber that is located within a rotor housing and is used to compress compressible fluids such as gases. The rotor has slots along its length, and each slot contains a blade, i.e. a vane. The vanes are thrown outwards (radially) by centrifugal force when the compressor is running and the vanes move in and out of the slot. The outer (radial) edge of the blades will follow the contour of the inner chamber wall, and the two side (axial) edges of the blades will each be adjacent to a side head plate of the compressor. The vanes thereby create individual cells or pockets of gas which, because of the vanes' movement, are compressed as the rotor turns. The vanes sweep the cylinder, sucking air in on one side and ejecting it on the other. As each cell approaches the discharge port, its volume is reduced and the compressed fluid is discharged. The compressor can be utilized to compress any gas, including air. (The use of the terms “radial” and “axial” and derivatives thereof as locations on a compressor blade of the invention are in reference to the blade's placement within a compressor.)

A major concern with sliding vane compressors is discharge temperature, which must be controlled within reasonable limits to avoid serious mechanical damage to the compressor. Uncontrolled discharge temperature can lead to thermal growth of internal components causing jamming, internal components degrading or melting and lubrication failure.

One cause of increased discharge temperature is the leakage of air from pocket to pocket within the compressor. As gas is compressed, its temperature will increase, so that gas within a compressor will be at its greatest temperature at the point of discharge from the compressor. If air from a compressor pocket leaks “backwards” to preceding pockets opposite the direction of movement of the rotor, the air temperature in a preceding pocket will increase, with the subsequent increase in the air discharge temperature as the pocket moves to the discharge point. With this cycle being continuously repeated, this will result in a steady increase in discharge temperature, causing the problems discussed above.

Poorly sealing blades are the main causes for leakage from a pocket that is at a higher pressure to an adjacent pocket that is at a lower pressure. Leakage across each blade becomes significantly greater when the compressor is designed to operate at higher discharge pressures, in which case the differential pressure across each blade increases. Numerous conditions may cause excessive leakage across a blade. The major sources for leakage are intermittent sealing contact of the blade tip at the cylinder wall, little or no axial sealing contact at the head plates located at both ends of the cylinder housing, and poor sealing contact in the rotor slot.

Leakage paths across the blade tip at the cylinder wall and within the rotor slot can be corrected by precision machining of the blade, cylinder, and rotor. This invention addresses the major leakage paths that are created by poor sealing at the head plates.

A significant leakage path is for air to travel from one pocket to an adjacent pocket in the area between an axial edge of a vane and an adjacent side head plate of the compressor. This leakage condition can exist at each head plate at both ends of the cylindrical cylinder. It is therefore an object of this invention to have a rotary vane compressor that provides a tight seal between the vanes and both compressor head plates.

In order to create a tight axial seal at head plates a multi-sectioned blade has been developed, in which the axial edges of the end sections are forced against the compressor's end plate. However, using a multi-sectioned blade may create its own disadvantage in that another significant leakage path is for air to travel from one pocket to an adjacent pocket at the joints between the multiple piece blade sections. It is therefore a further objective of this invention to have a joint at adjoining blade sections that provides a tight seal while automatically compensating for wear.

An oil flooded rotary vane compressor utilizes oil as both a lubricant and a sealant. An oil free compressor will typically utilize a self-lubricating blade. Such blades, however, are much more subject to wear then conventional compressor blades. If a worn blade breaks it can cause great harm to the compressor, and therefore it a further object of this invention to have a means of detecting advanced blade wear in a self-lubricating blade before a blade wears to the extent that it breaks and causes damage to the compressor.

DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawings. The drawings are not necessarily drawn to scale.

FIG. 1 is a sectional view, cut radially, of the interior of a sliding vane compressor having straight blades.

FIG. 2 is a sectional view, cut radially, of the interior of another embodiment of a sliding vane compressor having angled blades.

FIG. 3 is a longitudinal sectional view, showing a portion of one end of a sliding vane compressor cut in the axial direction.

FIG. 4 is a side elevational view of one embodiment of an assembled two piece compressor blade of the present invention as it would be installed in the compressor, with a portion of the tip depicted, and also depicting in relief an internally situated compression spring that is used to apply force axially to each blade piece.

FIG. 4A is a view from the direction of arrows C of a side edge of the blade of FIG. 4.

FIG. 5 is an isometric elevational view of a disassembled two piece blade of the present invention, depicting the primary sealing surfaces of the overlapping lap joint.

FIG. 6 is an isometric elevational view identical to FIG. 5, but depicting the secondary sealing surface of the overlapping joint.

FIG. 7 is a side elevational view, of a disassembled two piece blade with two compression springs.

FIG. 8 is a side elevational view of an assembled three piece blade with one compression spring at each overlapping joint.

FIG. 9 is a side elevational view of a disassembled four piece blade with one compression spring at each overlapping joint.

DESCRIPTION OF THE INVENTION

The above and other objects are realized by the present invention which provides for a multiple piece blade for use in a rotary sliding vane compressor. Each blade section is designed to provide ongoing sealing as the blade wears. The blade may be used in both oil lubricated and oil free compressors.

The blade utilized in the present application is made from multiple radially cut sections. It is a feature of the present invention that an axially directed force originating in the area in which the sections are joined is incorporated within the blade and is utilized, as the blade wears, to force adjacent blade sections apart from each other to thereby create a tight seal of the axial outer edges of the multi-sectioned blade against the head plates of the radial compressor. The force is applied automatically to adjust axially and compensate for thermal growth and blade wear while providing a seal of the blade against the head plate.

The blade is made from two or more radially cut sections that can accommodate a spring loaded feature. In one example, compression springs may be used to spread the blade sections axially to create a tight seal where the ends of the blade rub on the head plates. This spring loaded action automatically adjusts axially and compensates for thermal growth and blade wear. Manufacturing the blade out of two or more pieces is also a feature of the invention, as it is difficult to economically manufacture blades for large compressors in one single piece. Furthermore, long single piece blades are prone to warping, which will cause the blade to jam in the rotor slot. The blade will break if it can not move freely up and down within the rotor slot. Thus, it is preferable to manufacture a long blade from two or more shorter blade sections cut width-wise (radially) and not length-wise (axially).

Referring to the drawings by characters of reference, in FIG. 1 sliding vane compressor 100 is depicted, consisting of a housing in which there is enclosed an essentially cylindrical chamber 102 having an elongated cavity having a circular cross section, with a cylindrical rotor 101 having a circular cross section eccentrically and rotatably placed within chamber 102. Formed in rotor 101 is a plurality of radially extending grooves or slots 103 which extend from the surface 110 of the rotor to a point 111 in the interior of the rotor. Each of the slots accommodates a freely sliding blade or vane 104. The sliding vane compressor can utilize straight (as shown in FIG. 1) or angled (as shown in FIG. 2) rotor slots.

During rotation in the direction shown by arrow R of the rotor each vane 104 is thrown outwards by centrifugal force so that its outer edge sweeps the internal cylindrical surface 112 of chamber 102. The free space between adjacent vanes is thus divided into closed cells (such as 105, 106, 107). Inlet 108 and outlet 109 extend through housing 102. Air or other fluid at atmospheric pressure is taken in at stationary fluid inlet 108 in the direction of arrow A and is thus compressed as the free space in each cell diminishes as the rotor turns and the compressed air exits at stationary fluid outlet 109 in the direction of arrow B. Accordingly in the operation of a rotary vane compressor the closed cells to either side of any particular vane are at different pressures as the vane passes from the inlet port to the outlet port.

The present invention can be advantageously utilized on essentially any prior rotary vane compressor. Therefore, it can be used on rotary vane compressors having a rotor mounted in an elongated cavity which may be cylindrical with, for example, an essentially circular, elliptic, or epitrochoidal cross section formed therein. In certain prior art compressors the bore of the cavity can have an undercut in which the rotor sits lower in the housing in which case the cross section of the cavity would not be, for example, a perfect circle.

FIG. 2 illustrates a compressor similar to the compressor depicted in FIG. 1 with the exception that the rotor slots 203 are angled away from the center of the rotor. Angled slots allow deeper slots to be cut into the rotor profile while still providing a significant rotor core (the undisturbed center area of the rotor). Deeper slots are necessary to provide for wear allowance, especially in the case where lubrication is provided from blade wear. A significant rotor core provides the majority of strength and stiffness in a rotor. Excessive slot depth with slight or no slot angling will reduce the rotor core significantly, thus lowering the strength and stiffness of the rotor. The rotor may bend under load, thus creating a problem with operating at minimal clearance.

Another feature of angled slots is a portion of the centrifugal force acting on the blade is absorbed into the rotor slot. The blade tip does not rub on the same plane as the resulting centrifugal force acting on the center of gravity of the blade as it rotates about the axis of the rotor. This reduces rubbing pressure of the blade tip on the cylinder wall and the result is less wear at the blade tip, less frictional losses from the blade rubbing on the cylinder wall, reduced discharge temperature due to lower frictional heat, and less shaft power to operate the compressor.

If the blades of the present invention are utilized in an oil free compressor it is preferred that they be self lubricating. A self lubricating blade must wear to provide lubrication, and therefore will require a greater slot depth than a conventional compressor blade, since it is important to maintain sufficient engagement of the blade in the rotor slot or the blade might be thrown out of the slot, which can jam the compressor and cause breakage. Although the question of increasing slot depth without weakening the core of a rotor may be addressed by increasing the size of the rotor, this goes against the ideal of using the smallest compressor block to produce the greatest amount of compressed air. In view of the above, an angled slot may be preferred in an oil free compressor to provide significantly greater slot depth while providing an ample core area.

Typically, the angled slot will be at an angle of from about 1° to about 30° from a line that extends from a point on the center of the blade tip as the blade tip contacts the cylinder wall, the point of the maximum blade extension out of the rotor slot, with respect to the center of the rotor. Although increasing the slot angle provides the benefits of increasing the allowable slot depth, increasing the size of the undisturbed center core, and reducing frictional rubbing at the tip, it also increases the maximum distance the blade must extend out of the rotor slot. This requires the blade to be much stronger and larger, which greatly increases the mass of the blade and resulting centrifugal forces acting on the blade. As a result of diminishing returns, the preferred angle is from about 20° to about 25° and preferably about 22°.

With the rotation of the rotor, the blades are thrown outward toward the inner wall or surface (112, 212, with reference to FIGS. 1 and 2) of the cylindrical chamber. In both FIG. 1 and FIG. 2 the rotor is eccentrically placed within the cylindrical chamber of the compressor, and accordingly the outer surface (110, 210) of the rotor is variably placed from the inner surface of the cylindrical chamber. Accordingly, centrifugal force will throw the blade (104, 204) out of the slot (103, 203) the furthest in those regions of the compressor where the outer surface of the rotor is furthest from the inner surface of the cylindrical chamber. In those regions where the outer surface of the rotor is closest to the inner surface of the cylindrical chamber the blades may not significantly extend out from the slots.

Referring to FIG. 3, a compressor comprises a housing 300 having a cylindrically bored chamber 301 therein. End plates or walls 302 close the ends of the bore. Rotor shaft 303 is eccentrically rotatable in the bore 301 and is rotatably driven by a prime mover such as a motor (not shown). A circular cylindrical rotor 304 is fitted on the shaft 303 and is formed with radially extending slots. A blade or vane 305 is radially slidable through the slots so that rotation of the shaft 303 causes the rotor 304 and blade 305 to rotate therewith in a unitary manner. In the present invention the blade 305 extends past the edge 304 a of the rotor to form a tight seal on the head plate 302.

FIG. 4 illustrates a two-piece blade 400 of the present invention, having sections 403 and 404 that are radially aligned with each other at junction 411. Blade 400 is substantially rectangular in shape and has upper axial side 401 which, when the blade is operational in a compressor, is proximate to and in sealed engagement with internal cylindrical surface (112, 212) of compressor chamber (102, 202). Lower axial side 402 is under normal operational conditions always inserted within slot (103, 203). Radial sides or edges 408 of the blade will be abutting end wall or head plate 302 (FIG. 3) to form a seal to prevent air from leaking around the axial edge of a compressor blade into an adjacent pocket.

It is a feature of the present invention that there is a force applying means at the junction 411 of any adjacent blade sections that constantly acts upon the adjacent blade section pieces to force them apart from each other in an axial direction. For example, interior to the blade there can be at least one compression spring 407 which is biased to constantly force the two blade pieces 403 and 404 axially apart to thereby accordingly force each blade edge 408 into a sealing engagement with its adjacent head plate. As the edges wear the compression spring will continue to force the blade pieces further apart to thereby compensate for the wear and to keep the edges in a constant sealing relationship with the head plate.

In a preferred embodiment the upper portion 405 of the joint of the two blade pieces 403 and 404 comprises an overlapping lap joint in combination with a butt joint. Such a combination joint provides a seal in all potential planes of air leakage flow. For example—the vertical upper portion 405 of the lap joint provides a seal across the thickness (FIG. 4A, direction ←E→A) and along the length (axially, direction ←D→A), but does not provide a seal across the width (radially, direction ←F→A) of the blade. The horizontal lower portion 603 a and 603 b (see FIG. 6), at the base of the main overlapping joint 405 and transitioning to a butt joint, provides the seal across the radial width (direction ←F→). In the lower jointure portion 406 the two pieces 403 and 404 are preferably in a butt joint, end to end relation with each other, so that the composite lap joint and butt joint forms a S shaped joint. Preferably, when the blade is in operation within a compressor at least all of lower area 406 is located within the rotor slot. The advantage of this “S” type overlapping joint is that it provides a seal in all normally anticipated planes of leakage flow. For example, the joint provides a seal across the thickness, along the length, and across the width of the blade.

Alternatively, portions of the two (or more) blade pieces can be joined together by other type of edge joints such as tongue and groove joints, sliding slot joints, V-joints, dovetail joints, lap joints or a combination thereof.

FIG. 4 a shows one side edge of blade 400 as seen from the perspective of arrows C. Depicted is trailing surface 408 a and leading surface 408 b. With reference to blade tip 401 a, when a self-lubricating blade is utilized, the geometry of the machine (cylinder size, shape, rotor diameter, slot angle, etc) will cause the blade tip to eventually wear to the optimum profile. However, this will not happen in the short term with non-lubricating blades, as they will have better wear properties. In either scenario, if new blades are installed and the tip profile is not optimum there may be undesirable leakage over the blade tip (that is, the tip makes a poor seal). Thus, it is desirable to machine the optimum tip profile (as close as possible) into a new set of blades to minimize the break in period.

The material of construction of the blade will be dependent upon whether it is desired that the blade be self-lubricating. If the blade is not self-lubricating it can be constructed of, for example, a carbon-fiber resin composite, magnesium, aluminum or various reinforced resin bonded materials. If the blade is self-lubricating, materials of choice include solid graphite, composite graphite, or any other binder material with additives that provide lubrication. Lubrication additives include any dry lubricant that lowers friction such as PTFE, graphite, hexagonal boron nitride, molybdenum disulfide, and various plastic resins.

During operation the sections of the compressor blade remain forced apart, such as in the depicted example by the compressive spring force, in an axial direction as shown by arrows ←D→ on FIG. 4. As the blade wears pocket air will flow into the area between the separating portions. Preferably, the blade is machined with a joint that provides optimum sealing in the absence of oil. In this regard, when a combined lap joint/butt joint junction is utilizing as illustrated, air will flow down the area between the separating lap joint but will be stopped in the area formed by seal surfaces 603 a and 603 b (FIG. 6) where the lap joint transitions to a butt joint, which horizontal transitioning area acts as an air seal. The spring force may be either increased or decreased to thereby adjust the rubbing pressure of the blade against the head plates. If the rubbing pressure on the head plates is too light, there may not be a sufficient seal on the head plates, whereas if it is too heavy the blade will wear excessively along its length and in addition there will excessive frictional heat. In addition, the spring force will serve to provide a blade that automatically compensates for differences in thermal growth in the axial direction, that is, it will provide an adequate seal at the head plates independent of the operating temperatures.

Numerous means can be used to spread the blade sections. These include one or more compression springs, leaf springs, wave springs, air springs, or any other means that uses a mechanical means or differential pressure to create a spreading force. The spreading force can vary (such as with a compression spring) or be constant (as with an air spring) with respect to the amount of joint displacement.

The blade can also be constructed to be self spreading at the joint without the need for a spring or any other separate spreading device. The joint can be offset from the center of the blade (in the thickness direction) to provide unequal lateral areas within the joint. The larger area faces the higher pressure (leading side) of the blade and the smaller area faces the lower pressure (trailing side) of the blade. The pressure in the leading pocket is significantly higher than in the trailing pocket when sealing is required. The higher pressure in the leading pocket acts on the larger lateral area in the joint. The lower pressure on the trailing side of the blade acts on the smaller lateral area in the joint. This creates a spreading force at the joint that overcomes the opposing force at the blade ends that rub at the head plates. The result is a natural spreading force that automatically increases with differential pressure across the blade, providing optimum sealing at the head plates when needed most.

The combination of a lap joint and a butt joint has a further advantage. As the blade's upper surface becomes worn by contact with the internal cylindrical surface of the compressor chamber, the blade will gradually start to withdraw from the rotor slot. Eventually lower area 406 will extend out from the slot. Contemporaneously with the wearing of the blades upper surface 401, side edges 408 of the blade will also begin to be worn through contact with end plates 302. Adjoining surfaces 506 a and 506 b (FIG. 5) of the butt joint will separate as the axial forces drive sections 403 and 404 apart, and there will be leakage across the blade from the higher pressure pocket to the lower pressure pocket. This leakage is not necessarily completely detrimental, as excessively worn blades are likely to break independently of whether there is leakage across a blade. A broken blade can cause possible and perhaps significant mechanical damage within the compressor.

It is a feature of the preferred embodiment of the invention that when the self-lubricating blades of the present invention wear they are designed to cause leakage at a point before the wear becomes so excessive as to cause possible breakage; in effect at a predefined point of wear of said at least one blade there is a controlled leakage of air across the blade from one pocket to an adjacent pocket. This feature, coupled with the fact that high leakage across a blade will cause the discharge temperature of the compressor to rise significantly, results in a system of monitoring blade wear. Therefore, a preferred embodiment of the invention employs a compressor that utilizes multi-piece blades having a S shaped, combination lap and butt, joint coupled with a temperature sensor at the discharge of the compressor and a processor means that serves to automatically shut down the compressor when a specified temperature is reached. This feature can prevent significant mechanical damage to the compressor. Alternatively or in addition, the blade can be designed with one or more holes through its thickness that, when the blade is not worn or lighten worn, will always be within the rotor slot. As the blade is worn to a predetermined point these holes will become exposed to the air pockets and consequently air will leak therethrough from a high pressure pocket to a low pressure pocket. Thus, the blade of the present invention will not only automatically compensate for wear in the radial direction (by continuing to move further out of the slot with wear) but also in the axial direction. In addition to compensating for wear in the axial direction, the blade of the present invention automatically compensates for differences in thermal growth in the axial direction so that it will provide a seal at the head plates independent of the operating temperatures of the compressor. Further, the force of the axial blade side rubbing (due to the spreading force from the axially directed force) on the head plates mechanically pushes the blade into the rotor slot, opposing to a certain extent the centrifugal force throwing the blade out of the slot and lessening the rubbing pressure of the blade tip on the cylinder wall.

FIGS. 5 and 6 illustrate a disassembled two piece blade of the present invention having matching lap joint surfaces 501 a and 501 b, and pre-formed holes 502 a and 502 b for receiving a compression spring. As the blade pieces are forced apart axially, some of the pocket air may flow radially in the widening gap between the separating pieces in the direction of arrow F. The path of the air will be hindered by matching sealing surfaces 603 a and 603 b, which begins that portion of the blade in which there is a transition between a lap joint and a butt joint. The separation of matching surfaces 604 a and 604 b to the butt joint will not have a bearing on air flowing between adjacent pockets in a compressor, since those surfaces are typically located within the rotor slot under normal operation of the compressor of the invention.

FIG. 7 illustrates a disassembled two piece blade of the present invention having pre-formed holes 702 a, 702 b, 703 a and 703 b for receiving two compression springs 704. In certain instances more than two springs may be desirable between adjacent blade pieces or other type of springs may be used.

FIG. 8 illustrates an assembled three piece blade of the present invention having end segments 801 and 803 and middle segment 802. A compression spring 804 is located at each interlapping joint between adjacent blade sections.

FIG. 9 illustrates a disassembled four piece blade of the present invention having end segments 901 and 904 and middle segments 902 and 903. A compression spring 905 is located at each interlapping joint between adjacent blade sections.

Preferably, multi piece blade segments may be made interchangeable for all size compressors, assuming the blades have the same blade width and thickness. In such a case the end segments of the blades of FIGS. 8 and 9 are interchangeable with those of FIG. 4, and the middle segment of the blade of FIG. 8 are interchangeable with the middle segments of the blades of FIG. 9.

It is to be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims. 

1. A compressor blade for a rotary vane compressor having a rotor with blade receiving slots and a cylindrical housing having opposite head plates, said blade being substantially rectangular and having two opposed substantially radial sides and a first and a second opposed substantially axial sides, with said first side adaptable to being received in a slot of said rotor, said blade having at least two section pieces, with any two adjacent section pieces being radially aligned with each other at a junction, wherein the blade further comprises a force applying means at said junction forcing the adjacent blade section pieces apart from each other in an axial direction.
 2. The blade of claim 1 wherein the force applying means exerts a force sufficient to keep each radial side in a sealing relationship with an adjacent head plate of the cylindrical housing.
 3. The blade of claim 1 wherein the force applying means is located interior to the blade.
 4. The blade of claim 3 wherein the force applying means is at least one compression spring.
 5. The blade of claim 1 wherein the radially aligned section pieces are attached to each other by a combination joint comprising a lap joint that transitions into a butt joint, said butt joint being in the vicinity of the first axial side and said lap joint being in the vicinity of the second axial side.
 6. The blade of claim 5 wherein the combination joint provides an air seal in all potential planes of air leakage flow.
 7. The blade of claim 1 wherein said blade is self lubricating.
 8. A compressor blade for a rotary vane compressor having a rotor with blade receiving slots and a cylindrical housing having opposite head pieces, said blade being substantially rectangular and having two opposed substantially radial sides and two opposed substantially axial sides, with a first of said substantially axial sides being adaptable to being received in a slot of said rotor, said blade having at least two section pieces that are radially aligned with each other at a junction, wherein further the blade is self lubricating.
 9. The blade of claim 8 which is manufactured from graphite or a composite graphite.
 10. The blade of claim 8 further comprising means to automatically compensate for blade wear in an axial direction during operation within a rotary compressor.
 11. The blade of claim 8 further comprising means to mechanically push the blade into the rotor slot during operation within a rotary compressor.
 12. A compressor blade for a rotary vane compressor having a rotor with blade receiving slots and a cylindrical housing having opposite head plates, said blade being substantially rectangular and having two opposed substantially radial sides and two opposed substantially substantially axial sides, with one substantially axial side adaptable to being received in a slot of said rotor, said blade having at least two section pieces and further being self-spreading so that said section pieces will spread apart from each other in an axial direction during operation without the need for a separate spreading device such as a spring.
 13. A rotary sliding blade compressor comprising: a housing defining a closed cavity having an inner cylindrical wall and a pair of spaced parallel end walls; a slotted rotor eccentrically positioned within said cavity to define with said cylindrical wall and said end walls a compression chamber; a plurality of blades slidably mounted in the slots of said rotor; means to rotate the rotor about an axis to move said blades generally radially of the rotor toward and in sealed engagement with said cylindrical wall during such rotation; inlet ports for a gas to be compressed and outlet ports for compressed gas communicating with said compression chamber; said blades being substantially rectangular and having two opposed substantially radial sides and a first and a second opposed substantially axial sides, with said first side adaptable to being received in a slot and said second side being adaptable to being in a sealing relationship with said inner cylindrical wall, said blades forming pockets between the wall and rotor which vary in volume as the rotor rotates, with at least one blade having at least two section pieces, wherein any two adjacent section pieces are radially aligned with each other at a junction, wherein further there is a force applying means at said junction forcing the adjacent blade section pieces apart from each other in an axial direction so that the each radial side of the blade is constantly in a sealing relationship with an adjacent end wall.
 14. The compressor of claim 13 wherein the force applying means is located interior to the blade.
 15. The compressor of claim 14 wherein the force applying means is at least one compression spring.
 16. The compressor of claim 13 wherein the radially aligned section pieces are attached to each other by a lap joint that transitions into a butt joint, said butt joint being in the vicinity of the first axial side and said lap joint being in the vicinity of the second axial side.
 17. The compressor of claim 13 wherein said at least one blade is self lubricating.
 18. The compressor of claim 17 wherein at a predefined point of wear of said at least one blade there is a controlled leakage of air across the blade from one pocket to an adjacent pocket.
 19. The compressor of claim 18 further comprising means to detect said controlled leakage of air. 